DCN: 141-00940-02 7/14/03
10
Heat Pump HVAC System Setup
Heat Pump Mode Selection.
For Heat Pump operation, set SW1-1 to the HP SYS position (ON).
Fan Mode Selection.
Set the Fan selection, SW1-2, to the STD FAN position (OFF).
Change Over Selection.
Heat pump systems change from heating to cooling by reversing the direction of
Freon flow in the system. This change over is controlled by the CHANGEOVER (CO) output from the Control
Unit (sometimes this is referred to as the reversing valve).
Most heat pump systems are designed to work normally in the heating mode and require a change over
output for cooling. Set dipswitch SW1 position 3 to the CO/CL position (SW1-3 = OFF) for this type system.
Check your HVAC system requirements for correct settings.
If your system requires changeover with heating, set SW1 position 3 to the CO/HT position (SW1-3 = ON).
Changeover Relay Operation:
The changeover relay output stays ON after a heating/cooling call for the
duration of the minimum off delay period. If another call occurs before the delay period expires, the CO relay
will already be on and this avoids continuously cycling the CO valve on/off for each call.
TXB16 Control Unit HVAC System Outputs for Heat Pump Systems
Operating Mode
Changeover with Cool
Changeover with Heat
Manual Fan
G
G
Heating Stage 1
Y1, G
Y1, G, O
Heating Stage 2
Y1, Y2, G
Y1, Y2, G, O
Heating Stage 3
Y1, Y2, G, W1
Y1, Y2, G, O, W1
Cooling Stage 1
Y1, G, O
Y1, G
Cooling Stage 2
Y1, Y2, G, O
Y1, Y2, G
Emergency Heat
W1, G
W1, G
Control Unit Status LEDs
The Control Unit has LEDs on the circuit board to show system status and output states. The STATUS LED
will normally blink on and off slowly as a system heartbeat. During MRT/MOT delay periods, the STATUS
LED will blink twice for each heartbeat. The other LEDs indicate the operation of the control unit output
relays. When the LED’s are on, the output relay is on.
LED
Function
Control Unit Output
H1
Heat stage 1 output (Heat stage 3 for HP systems)
W1
Fan
Fan output
G
C1
Compressor stage 1 output
Y1
C2
Compressor stage 2 output
Y2
H2/CO
H2 =
Heat stage 2 output for Standard HVAC systems
CO
= Changeover valve output for Heat Pump HVAC
systems.
W2
O
